This invention relates to paperboard containers of the type often used for the packaging of liquids such as milk and fruit juices. Such containers are fashioned from a unitary blank of paperboard, usually coated on both its interior and exterior forming surfaces with one or more barrier layer materials, cut and scored, erected and filled on automatic machinery to form gable top liquid packages. Such containers have a flat bottom and a gable top upper or roof section, the latter being adapted to form a pour spout when opened, all as known. An intermediate step in making such containers is the formation of a tube structure from the blank, with the steps of forming the end closures and filling with liquid taking place after tube formation.
In the formation of a gable top containers from a unitary blank having a plurality of wall forming panels serially arranged, one step involves forming a tube by folding the blank so that the fifth or sideseam forming panel is superposed over an edge zone of the free edge portion of the first sidewall forming panel. A part of the carton interior forming surface of the first panel has been heated so as to partially melt the usual polyethylene coating and make the latter sticky. Similarly, that portion of the fifth or sideseam panel which is to be in surface contact with the first panel free edge zone has also been heated so as to make its polyethylene coating sticky. The transverse cross sectional configuration of the now folded blank is substantially that of a shallow diamond, with a force applied to the upper two panels collapsing the diamond shaped tube, resulting in a force applied to the sideseam flap or panel to seal it to the edge zone portion of the first panel.
Often, the sideseam is skived, with the particular skiving process/apparatus employed unavoidably resulting in a taper at one end of the sideseam forming or fifth panel, at the bottom carton closure. This taper causes a partial triangular uncovering of the first panel edge zone, so that when the first and fourth panels are pushed downwardly to compress and seal the sideseam (fifth) panel against an edge zone of the second panel, a portion of the second panel will contact an exposed hot and sticky triangular portion of the first panel and cause an unwanted adhesion between a triangular portion of the first panel, near the tapered end of the sideseam panel, and the triangular portion of the second panel. In order to avoid this unwanted adhesion, the temperature of the heated first panel edge portion and the temperature of the fifth or sideseam forming panel was reduced to reduce the stickiness. While solving the problem of unwanted adhesion, such temperature reduction diminished the strength and quality of the seal between the sideseam panel and the first panel. This lowered quality becomes unacceptable with extended shelf life liquid cartons.